330 ^ NATURE AND MAN. 



" into the denser layers of our atmosphere. In tracts where the 

 "growth of silt upon the sea-floor is excessively tardy, the fine 

 "particles scattered by the dissipation of these meteorites may 

 "remain in appreciable quantity. It is not needful to suppose 

 "that meteorites have disappeared over these ocean-depths more 

 "numerously than over other parts of the earth's surface. The 

 "iron granules have no doubt been as plentifully showered down 

 "elsewhere, though they cannot be so readily detected in accumu- 

 " lating sediment. I know no recent discovery in physical geo- 

 "graphy more calculated to impress deeply the imagination than 

 "the testimony of this meteoric iron from the most distant abysses 

 " of the ocean. To be told that mud gathers on the floor of those 

 "abysses at an extremely slow rate conveys but a vague notion of 

 "the tardiness of the process. But to learn that it gathers so 

 ** slowly that the very star-dust which falls from outer space forms 

 "an appreciable part of it, brings home to us, as hardly anything 

 " else could do, the idea of undisturbed and excessively slow 

 "accumulation." — Lecture on Geographical Evolution^ p. 7. 



Next to the volcanic clays, the globigerina-ooze (which had 

 been brought up by the hundredweight in the Lightning and 

 Porcupine dredgings) proved to be the most abundant oceanic 

 deposit. Not only from the completeness of their minute shells 

 in the surface-layer, but also from the fact that a large proportion 

 of these shells were occupied by their sarcodic bodies in an ap- 

 parently fresh condition, we had concluded that the Globigerinae 

 live on the bottoms on which their remains accumulate. But 

 since, in nearly all but the coldest parts of the oceanic area 

 traversed by the Challenger, they were collected in abundance 

 by the " tow-net " drawn through the waters at or beneath the 

 surface. Sir Wyville Thompson and some of his associates have 

 come to the conclusion that they pass their whole lives in the 

 surface stratum, their subsidence to the bottom only taking place 

 after their death, I have myself, however, remained of the 

 ojjinion that they subside during life, when the addition of new 

 chambers has come to an end, and the further exudation of car- 

 bonate of lime has been applied to the thickening of the walls of 

 the old ; and that they continue to live on the bottom, continually 

 adding to the thickness of their shells. And in this I have the 



